garrett376

Interesting - the guy at a seal place (and on the link below) told me EPR and EPDM are the same thing...

The current seals are blue - the only seals that show as blue on this chart, are Silicone. Maybe that's the material I need instead of EPDM (which is what most clutch rebuild kits use)...

http://www.epm.com/sealsfast_materials.htm

kgorman

Garrett, I started working a parallel path since our discussion. I was thinking we would have to give the specs to a seal mfr and they would have to create the seals for us. I am just worried we will have to buy a metric-sh%$^ ton of them to make them cost-effective. I will post what I find out as well, I will make some calls today.

kgorman

Are you sure about this? I can't remember if my tech changed the tranny fluid because he actually saw that is was contaminated or was just trying to be careful.

kgorman

regarding materials, I was looking at this:

http://www.efunda.com/designstandard...ng&CO=alfa#mat

Indycam

"Trying to find the exact seal that fits AND with dimples will be tough but I am listening (er, reading) and rooting for you. "
I guess that the ones with dimples are not seals , I guess they are anti friction .

"But I wonder about the pressure difference of a braking system vs. the PDAS..."
I guess its 3000ish psi .

kgorman

I spoke to these guys: http://www.oringswest.com/. It seems they most likely can provide what we need, but there are many questions that need to be answered.

- this is a high friction part, so it a regular seal going to work?
- perhaps we do not try to match the existing material, but try to use a more modern equiv?
- EPDM seems like the right choice, but the guys at oringswest mentioned that we can not use sulfer-cured, only poly cured EPDM.
- look at Garretts pics, as Indycam points out those outside 'seals' might be just for gliding on, if so, is the interior one the only one we need to source? My outside seals also have the diagonal cut, so I believe they are supposed to be a U an not a O. Garrett is this your expectation?
- any custom mgfr seal will likely cost $250+, we won't know how many units we get until we spec what we want.
- so hopefully we have a std type/size here or perhaps we might need to group by it to make it cost effective.

Indycam

The problem for me is selling the part after you get a bunch . If you do not insure yourself , you could be on the wrong end of a law suit . Building and selling car parts is a legal nightmare . The part you are looking to fix up with an aftermarket part , is critical to safety .

http://www.cdnn.info/news/safety/s060526.html

JasonAndreas

I've purchased liquid silicone (from Dow) in several colors including clear; polyurethane in a range of colors and I've seen viton and others elastomers compounded in every color under the sun. So don't base the material selection on color alone. Porsche could have spec'ed these seals in anything, they ordered well over 100,000 of them. Also, these seals sit on the transmission so the in-use service temperature required might rule out EPDM, unless filled. Definitely take up RicardoD on his offer. Another option is to find someone (there are a couple guys on Rennlist) that has or had access to the spec sheets that Porsche uses for materials and provides to their suppliers. I've seen them for fasteners and thread sealants but not actual seals.

Red rooster

Sorry to keep on but Porsche did not make the cylinders or seals !
I am trying to find the parts company that manufactured .
That will help lead to a parts dept , maybe !

Geoff
----------------------------------------------------------------
KS400200,the oldest 964 on Rennlist,unless you know differently !

Indycam

Red rooster
Can you look around for a shaft seal for a hydraulic C4 pump ?
The thing is made by ATE .

jjbunn

It's possibly not relevant, but when I rebuilt the brake master cylinder on my MGB the seals in that were made from plain old-fashioned rubber. They were also a very particular shape: not at all a simple O ring.

Looking at garrett376's photo of the disassembled cylinder reminded me :-)

garrett376

Very interesting thought Kenny - when I first disassembled the cylinder I thought it leaked because of the broken #1 and #3 seal thingies. So you think these two seals are supposed to be broken? I'll have to look more closely to see if they appear to be "stress fractured" or cut cleanly. I might take it to the office and look at it under the operating microscope! The key is whether the angulation of the cut is the same in all samples.

If that's the case, then it looks like replacing the middle seal will do the trick. I can't imagine it's a "high friction" environment that would cause any more issue than a brake or clutch cylinder. The slave is under the same conditions as the clutch slave cylinder, which I would think is similar to other clutch slaves which use regular o-rings made of EPDM. An EPDM o-ring to fit the piston groove is available and costs just $2. Tomorrow I will order several (one metric equivalent and one standard, since they are sized slightly different) and see how they hold up. At $2 per seal, even if it just lasts 1-2 years, it would certainly be worth it!

Kenny - with regards to the slave cylinder leaking its fluid into the tranny - think about when the slave is removed, no gear oil leaks out, right? So why would the brake fluid leak in? If the slave fails it has a drain hole out the bottom (lateral slave) to drain from; the longitudinal just gets all wet out the hole you used to poke out the piston. As long as the sealing boot is fine (which means no gear oil leaks out either) there is no reason that brake fluid would end up in your transmission. I think that PCA Panorama article is causing more waves of speculation!!

garrett376

The plot thickens, or thins...

So I decided to go for it and dig deeper... it is an o-ring!!! This plastic collar covers an o-ring. While it's hard to remove the plastic collar, and I may have stretched it beyond recovery, it seems like a new o-ring might cure the leaks. Odd, but that's really all I can assume! The o-ring looks fine - I've seen some worn o-rings and they're usually worn flat. So my plan is to order a EPDM 11x1.5mm o-ring and see how it works!

This plastic collar maybe prevents wear of the o-ring hiding below. Seems like that would not seal too well, but maybe it does as long as the o-ring provides proper pressure against it.

The angulation of both of the C-shaped blue sliders seem constant, so it seems they are supposed to be "split". I guess that's good news - it seems like a new replacement o-ring is an order!!!

The o-ring dimensions are:
ID = 11.1mm
cross-sectional width: 1.5mm
Piston groove diameter: 11.4mm

garrett376

I've been researching more than I thought I ever would... it appears that those two C-shaped things are called "wear rings" or "wear bands" and serve to decrease wear on the piston and piston seal and act as guides for the piston through the bore. Fascinating!!!

I found a place that has 11mmx1.5 o-rings:
http://www.epm.com/metric_chart1.htm

I'll call tomorrow to see if they have the EDPM material.


As a side note it's interesting how much brake fluid can drain out of the open slave cylinder line!!! My cup was just the right size!!!!

kgorman

Garrett,

I can verify the 'split' wear-rings are supposed to be that way. I took apart my good cylinder and it has the same design. I should have mentioned the black o-ring, I have that on mine as well. It was very clear on mine when it failed that the inner blue ring failed, but the o-ring was OK. Garrett, what part of your is leaking? I can't tell?

Hey, did you sell your NB 964? Can't you pull those and inspect those cylinders too?